Pump distribution network for multi-amplifier modules

ABSTRACT

An integrated optical device is provided for distributing optical pump energy. The device includes at least one input port for receiving optical energy, a plurality of output ports, and a user configurable optical network coupled to the input port for distributing the optical energy among the output ports in a prescribed manner in conformance with a user-selected configuration.

FIELD OF THE INVENTION

[0001] The present invention relates generally to planar waveguidecomponents that can be used to simultaneously provide optical pump powerfor a number of independent optical amplifiers.

BACKGROUND OF THE INVENTION

[0002] Modern telecommunications rely heavily upon transmission of lightsignals across long spans of optical fiber. As the light propagates froma transmitter to a receiver through the optical network, it loses energy(primarily due to light scattering) in the transmission fiber itself andalso (by more general loss mechanisms) in the other fiber-opticcomponents of the network. In order to compensate for this energydepletion, the optical power of a signal is repeatedly amplified byoptical amplifiers. An erbium-doped fiber amplifier, or EDFA, whichamplifies optical signals in the wavelength range from about 1520 nm to1620 nm, has become an integral part of most modern optical networks.This is discussed, for example, in the new volumes (IIIA and IIIB) ofthe series “Optical Fiber Telecommunications”, edited by I. P. Kaminowand T. L. Koch, Academic Press (1997). The increasingly common use ofEDFA's in this context now often leads to a situation where it isdesirable to have more than one amplifier at a single location in thenetwork. It has therefore been proposed to use in such instances specialmodules incorporating multiple separate amplifiers, or amplifier arrays.Examples of arrayed rare-earth doped amplifiers are described in “PlanarEr— and Yb-doped amplifiers and lasers” by Balslev, S.; Dyngaard, M.;Feuchter, T.; Guldberg-Kjaer, S.; Hubner, J.; Jensen, C.; Shen, Y.;Thomsen, C. L.; Zauner, D. Applied Physics B v.73(5-6), pp.435-438,2001, and in “New WDM amplifier cascade for improved performance inwavelength-routed optical transport networks” by Olivares, R.; Baroni,S.; Di Pasquale, F.; Bayvel, P.; Anibal Fernandez, F. Optical FiberTechnology v.5(1), pp.62-74, 1999.

[0003] An erbium-doped waveguide amplifier, or EDWA (a recent example ofwhich has been described in U.S. Pat. No. 6,157,765 by A. J. Bruce andJ. Shmulovich), has properties similar to those of an EDFA, andtherefore its functionality is equally important. However, unlikeEDFA's, EDWA's are waveguides manufactured on planar substrates usingglass hosts that may differ dramatically in composition from those usedin EDFA's. Although generally somewhat less efficient than EDFA's, inmany instances EDWA's have advantages compared to their fiber analogs:for example, a packaged EDWA chip has much smaller size than a packagedEDFA. Moreover, it is natural and straightforward to integrate an EDWAwith other passive or active optical components on the same planarsubstrate, an assembly that is impossible with EDFA's. Also, in someinstances the integrated module may be able to perform functions thatare not achievable by its modular fiber-optic analog.

[0004] Typically, at least two kinds of optical energies are present inEDFA's and EDWA's: first one is that of one or more signals withwavelengths from around 1520 to 1620 nm, the second one is that of oneor more optical pumps with wavelengths around 980 nm and 1480 nm. Thepurpose of the pump light is to deliver energy to Er ions in an EDFA andexcite them; a part of that energy is subsequently transferred to thesignal light resulting in its amplification. Amplifier arrays becomeespecially attractive when the number of required pump sources is lessthan the number of individual amplifiers. For instance, if a single pumplaser is used to simultaneously provide pump power for four separateamplifiers, it could potentially result in four-fold savings in pumpcost. U.S. Pat. No. 6,008,934 by Fatehi et al. describes a moduleincorporating several essentially independent amplifiers and pump powersplitters. The latter splitters provide fixed and equal pump powerdistribution among all the amplifiers, thereby making theminterdependent and prohibiting independent gain control in separateamplifiers. Therefore, the use of such a module is limited only tonarrow band, single channel amplification. In order for this module tobe useful in broad band applications utilizing severalwavelength-multiplexed channels, each amplifier has to be provided witha means of independent gain control. Typically, this is accomplished byvarying the pump power, which so far could only be achieved by providingeach amplifier in the amplifier array with a separate pump laser.

SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, an integrated opticaldevice is provided for distributing optical pump energy. The deviceincludes at least one input port for receiving optical energy, aplurality of output ports, and a user configurable optical networkcoupled to the input port for distributing the optical energy among theoutput ports in a prescribed manner in conformance with a user-selectedconfiguration.

[0006] In accordance with another aspect of the invention, the at leastone input port comprises a plurality of input ports and the opticalnetwork further comprises at least one optical mixer optically coupledto the plurality of input ports. The optical mixer is optically coupledto the plurality of output ports for incoherently mixing the opticalpump energy among the plurality of output ports.

[0007] In accordance with another aspect of the invention, the opticalnetwork further comprises at least one optical splitter opticallycoupled to the input port. The optical splitter is optically coupled tothe plurality of output ports for distributing the optical energy amongthe output ports.

[0008] In accordance with yet another aspect of the invention, theoptical network further comprises at least one variable opticalattenuator optically coupled to at least one of the ports for providingvariable attenuation thereto.

[0009] In accordance with another aspect of the invention, the opticalsplitter is a variable optical splitter for dividing the optical pumpenergy among the plurality of output ports in a user-prescribablemanner. In accordance with another aspect of the invention, the opticalnetwork is formed from a planar lightwave circuit.

[0010] In accordance with another aspect of the invention, at least tworare-earth doped optical waveguides are provided for receiving theoptical pump energy from the optical network.

[0011] In accordance with another aspect of the invention, therare-earth doped optical waveguides define individual stages of amultistage optical amplifier in which optical signal power from onestage is coupled into the other stage.

[0012] In accordance with another aspect of the invention, at least onepump source is coupled to the input port such that optical power isdistributed from the pump source to the rare-earth doped opticalwaveguides.

[0013] In accordance with another aspect of the invention, at least oneof the optical rare-earth doped optical waveguides is a planarwaveguide.

[0014] In accordance with another aspect of the invention, at least oneof the optical rare-earth doped optical waveguides is a planar waveguideand the other optical rare-earth doped optical waveguide is a fiberwaveguide.

[0015] In accordance with another aspect of the invention, therare-earth doped optical waveguides are rare-earth doped optical fibers.

[0016] In accordance with another aspect of the invention, the opticalnetwork and the two rare-earth doped optical waveguides are formed on acommon substrate.

[0017] In accordance with another aspect of the invention, a planaroptical device provides optical amplification. The device includes afirst plurality of signal input waveguides each receiving an opticalsignal, at least one pump input waveguide receiving optical pump energy,and a plurality of rare earth doped waveguides. A plurality of couplingwaveguides respectively couples the optical signal and the optical pumpenergy to the plurality of rare earth doped waveguides. A plurality ofoutput waveguides are coupled to the rare earth doped waveguides forproviding a plurality of amplified optical signals to an externalelement. The first plurality of signal input waveguides, the pump inputwaveguide, the plurality of rare earth doped waveguides, the pluralityof coupling waveguides, and the plurality of output waveguides areplanar waveguides formed on at least one substrate.

[0018] In accordance with another aspect of the invention, the firstplurality of signal input waveguides, the pump input waveguide, theplurality of rare earth doped waveguides, the plurality of couplingwaveguides, and the plurality of output waveguides are planar waveguidesformed on a common substrate.

[0019] In accordance with another aspect of the invention, the firstplurality of signal input waveguides, the pump input waveguide, theplurality of rare earth doped waveguides, the plurality of couplingwaveguides, and the plurality of output waveguides are planar waveguidesrespectively formed on a plurality of different substrates.

[0020] In accordance with another aspect of the invention, at least twoof the plurality of rare earth doped waveguides are configured fordifferent performance applications.

[0021] In accordance with another aspect of the invention, the differentperformance applications include optical pre-amplification and opticalpower amplification.

[0022] In accordance with another aspect of the invention, an opticaldevice provides optical amplification. The device includes a firstplurality of signal input waveguides each receiving an optical signal,at least one pump input waveguide receiving optical pump energy, and aplurality of rare earth doped waveguides. At least two of the pluralityof rare earth doped waveguides are configured for different performanceapplications. The device also includes a plurality of couplingwaveguides respectively coupling the optical signal and the optical pumpenergy to the plurality of rare earth doped waveguides. A plurality ofoutput waveguides are coupled to the rare earth doped waveguides forproviding a plurality of amplified optical signals to an externalelement.

[0023] In accordance with another aspect of the invention, the differentperformance applications include optical pre-amplification and opticalpower amplification.

[0024] In accordance with another aspect of the invention, thedifferently configured rare earth doped waveguides have at least onedifference selected from the group consisting of cross-sectionaldimension, length, dopant concentration, and composition.

[0025] In accordance with another aspect of the invention, the firstplurality of signal input waveguides, the pump input waveguide, theplurality of rare earth doped waveguides, the plurality of couplingwaveguides, and the plurality of output waveguides are optical fiberwaveguides.

[0026] In accordance with another aspect of the invention, at least onewaveguide, selected from among the first plurality of signal inputwaveguides, the pump input waveguide, the plurality of rare earth dopedwaveguides, the plurality of coupling waveguides, and the plurality ofoutput waveguides, is an optical fiber waveguide.

[0027] In accordance with another aspect of the invention, a method isprovided for distributing optical pump energy. The method begins byreceiving optical pump energy at an input of an optical network. Inaddition, the optical network is configured for distributing the opticalpump energy among a plurality of output ports in a prescribed manner.

[0028] In accordance with another aspect of the invention, the opticalpump energy is incoherently distributed among the plurality of outputports.

[0029] In accordance with another aspect of the invention, the opticalenergy is distributed among the output ports in a user-prescribablemanner.

[0030] In accordance with another aspect of the invention, a method isprovided for amplifying optical signals. The method begins by directinga first optical signal and optical pump energy to a first rare-earthdoped waveguide for providing optical gain to the first optical signal.The first erbium-doped waveguide are formed on a planar substrate. Asecond optical signal and optical pump energy are directed to a secondrare earth-doped waveguide for providing optical gain to the secondoptical signal. The second waveguide is formed on the planar waveguide.Finally, the optical pump energy received from a pump source is splitprior to directing it to the first and and second erbium-dopedwaveguides.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 A few schematic configurations of N×M network layouts thatcan be implemented using planar network technology.

[0032]FIG. 2 Schematics of (a) a directional coupler and (b) aMach-Zehnder interferometer as respective examples of configurable andre-configurable power-splitting networks.

[0033]FIG. 3 Schematic of a 3×5 power splitter providing equal power tofive variable optical attenuators.

[0034]FIG. 4 Diagrammatic representations of some opticalpower-distribution configurations that illustrate embodiments of theinvention.

[0035]FIG. 5 An example of a variable pump-power distribution networkfor an amplifier array module.

[0036]FIG. 6 schematically illustrates the layout of the basic EDWAtransceiver module of the present invention.

[0037]FIG. 7 exemplifies the performance of a representative EDWA asmeasured by its small-signal gain and noise-figure as a function a pumppower.

[0038]FIG. 8 schematically illustrates several other possible moduleconfigurations that utilize the basic principles of the presentinvention.

DETAILED DESCRIPTION

[0039] The invention describes an integrated planar-waveguide deviceincorporating a configurable pump power distribution network and severalseparate optical amplifiers. In general, the device has N pump inputports and M amplifiers, where N is less than or equal to M. Theessential function of this device is to couple optical power from one ormore pump laser sources into its N inputs and provide a prescribeddistribution of output power into its M amplifiers. In this manner thedevice is able to make an efficient use of amplifier arrays and othermulti-amplifier modules.

[0040] The general layout of an N×M network (101) with N inputs (102)and M outputs (103) is shown in FIG. 1(a). Many examples of such anetwork have been implemented using planar waveguide technology—from thesimplest 2×2 directional coupler (see for example “Theory of DielectricOptical Waveguides” by D. Marcuse, Academic Press, Boston, 1991) shownin FIG. 1(b) to more complex multimode interference, or MMI, couplers(see for example “Optical Multi-Mode Interference Devices Based onSelf-Imaging: Principles and Applications” by L. B. Soldano and E. C. M.Pennings, J. Lightwave Tech. 13(4), pp.615-627, 1995) shown in FIG.1(c). Reconfigurable N×M networks have also been proposed, which ingeneral provide arbitrary power splitting ratio between N input portsand M output ports. A configurable network can be realized using, forinstance, directional couplers or Mach-Zehnder interferometers (MZI's).A directional coupler can be configured to provide an arbitrary powersplit between its two output ports; however, after this coupler ismanufactured in a particular configuration, this configuration cannot bechanged. A MZI can provide means for obtaining a re-configurablesplitting ratio: as shown in FIG. 2(a), it can produce any splittingratios from 100% of power in the 1^(st) port (201) to 100% of power inthe 2^(nd) port (202) by varying the optical phase in one arm withrespect to the phase in the other arm. A more generalized approach tovariable splitting between M outputs using MZI's is described in“Analysis of Generalized Mach-Zehnder Interferometers for Variable-RatioPower Splitting and Optimized Switching” by N. S. Lagali et al. J.Lightwave Tech. 17(12), pp.2542-2550 (1999) and shown in FIG. 2(b).Alternatively, as shown in FIG. 3, one could use a fixed N×M network(301) to provide an equal power distribution among its M outputs, whichare then followed by M independent variable optical attenuators, orVOA's (302). This is a less energy-efficient design since each VOAdiscards part of the optical energy. However, this approach does greatlysimplify the control of power splitting and could easily be applied toall cases of re-configurable power distribution.

[0041] The emissions from two or more separate lasers emittingindependently are usually mutually incoherent (i.e. having no fixed andstable phase relationship) even when the emission wavelengths are veryclosely spaced. Therefore, a special optical mixer may be required thatevenly distributes power from N input power sources among its M outputports. By definition, such a mixer is an incoherent mixer. Its designcan be based on a fixed power distribution network, such as thatdepicted in FIG. 1(a), which divides the optical power at each of its Ninputs into M equal parts and evenly distributes these parts among eachof its M outputs. For example, the incoherent mixing of N one-Wattsources will produce N/M Watts at each output port. One more specificexample of such a mixer could be 3×3 MMI coupler with the length equalto L_(π)/3, where L_(π) is the MMI coupling length. In the case, whenthree incoherent sources are present at the three inputs of this MMIcoupler, optical energy at each input is equally split into three partsand distributed among the three outputs of the mixer. Generally, thereis some wavelength dependence for an equal power splitting to eachchannel. Therefore, in order to obtain an accurate even-powerdistribution, the emission wavelengths of the mixed sources should bewithin the spectral range defined by the wavelength-independence rangeof a particular mixer design.

[0042] A proposed optical distribution network may, in general, includeone or more of the following components: (1) a mixer having at least twoinput ports and at least two output ports, (2) a splitter having atleast one input port and at least two output ports, and (3) a variableattenuator having at least one input port and at least one output port.The mixer is required if two or more incoherent sources are used in thedistribution network; it distributes all input optical energy evenly (orunevenly, if required) among its output ports. The splitter or splittersarbitrarily redistribute this optical energy among their output ports.The splitters may be of the ‘fixed’ type, with power splitting ratiopredetermined by design and fixed during fabrication, or they may be ofthe ‘variable’ kind, for which splitting ratios can be dynamicallyadjusted during the operational lifetime of a device. Variableattenuators are used to reduce power going through one or more ports.They could be positioned anywhere in the network. Diagrams in FIG. 4illustrate some of the embodiments of the invention.

[0043] The primary application of a re-configurable optical distributionnetwork is likely to be in amplifier array modules, where it can beutilized as a pump distribution network. In addition to EDFA's andEDWA's, other types of optical amplifiers may benefit from a pumpdistribution network such Raman amplifiers, Pr-doped amplifiers,Tm-doped amplifiers and others. Another application of the inventionmight be in optical broadcasting, where an optical signal is split intomany parts and arbitrarily distributed among many ports. Also, since theproposed network in general contains an incoherent mixer, it could serveas a cheap wavelength multiplexer in WDM networks.

[0044]FIG. 5 illustrates one possible embodiment of such an invention.The module in FIG. 5 incorporates N input pump ports, M input signalports, an N×M pump distribution network with M controls, M pump-signalcouplers, M optical amplifiers, and M output signal ports. The controlsin the pump distribution network allow variability in pump distributionamong M amplifiers and thus their separate gain control. The amplifiersin this arrangement do not have to be identical. These amplifiers couldbe either single channel, narrow band, or broadband amplifiers. Theycould be either completely independent or somehow tied to each other.For example, in the case where M=3, amplifier 1 through 3 could be the1^(st), 2^(nd), and 3^(rd) stages of a 3-stage in-line EDFA. In thiscase, the 3 amplifiers would be connected in series with the output ofone feeding into the input of the next.

[0045] The concept of pump distribution could be implemented using bothplanar waveguide and regular fiber-optic technologies. However, theplanar lightwave circuit (PLC) technology appears to be better suitedfor its implementation, since it is capable of cost effectivelyintegrating many different optical components into one device. However,hybrid approaches may be beneficial as well. For example, one could usea PLC pump distribution network in combination with fiber-basedamplifiers such as EDFA. In this configuration the PLC chip allowsefficient pump distribution which is not easily achievable withfiber-optic components, whereas the EDFA's may perform better than theirplanar waveguide counterparts EDWA's in some applications.

[0046] In some instances an amplifier array may not require a variabledistribution network. Instead, a designer may know in advance therequired splitting ratio of pump energy going into the amplifier arrayand therefore use a fixed pump distribution network. Such a case isillustrated below for a transceiver module built upon a single PLC chip.

[0047]FIG. 6 schematically shows the layout of an EDWA transceivermodule exemplifying the present invention. In general, there may beseveral optical signals requiring amplification in the transceiver. Atleast one of the signals is an outgoing signal 601 from the transmitter602. Its source is a low power single-mode distributed-feedback (DFB)laser with a wavelength tuned to one of the InternationalTelecommunications Union (ITU) grid channels in the C-band. Therelatively low power of a DFB-laser limits the transmission range ofsuch a signal. However, this range can be significantly increased byraising the optical output power of the transceiver by means of apower-booster amplifier. In addition, at least one of the signals is anincoming signal 603 to the receiver 604. This receiver might typically,for example, be a PIN-detector with a sensitivity of about −19 dBm. Itis known that a sensitivity of this order can be improved by at leastabout 15 dB using an EDWA pre-amplifier (see, for example, “Highsensitivity receiver with an Er-doped waveguide preamplifier”, by A.Bruce, C. Bower, G. Weber, A. Hanjani, S. V. Frolov, A. Paunescu, T-MShen, J. Shmulovich, R. Durvasula and M. Itzler (submitted toElectronics Letters)). This, in turn, will increase the usefultransmission range for the incoming optical signal.

[0048] The module is comprised of several optical components based onboth planar-waveguide and free-space technologies. The planar waveguidesare all monolithically integrated onto a single substrate 606, such assilica on silicon. Fibers 601 and 603 in this example are respectivelycoupled to waveguides 625 and 608 via microlens pairs 613/614 and611/612, so that bulk isolators 611 and 610 can be placed between themicrolenses as shown in FIG. 6. Transmitter laser 602 and pump laser 605are coupled to waveguides 607 and 609, respectively, via a shortsections of lensed (e.g. U.S. Pat. No. 5,774,607, etc.) single-modefiber 617 and 616, while receiver 604 is coupled to the planar waveguide626 using a microlens 615. The pump power in waveguide 609 is split bythe power splitter 620, with about ⅔ of the pump power being directedtowards the booster-amplifier section (composed of waveguide 607,pump-signal combiner 618, Er-doped waveguide 621, pump-kill filter 623and output waveguide 625) and the remaining ⅓ directed towards thepre-amplifier section (composed of waveguide 608, pump-signal combiner619, Er-doped waveguide 622, pump-kill filter 624 and output waveguide626).

[0049]FIG. 7 shows the increase of small-signal gain and decrease ofnoise-figure NF for a representative EDWA as a function of increasing(978 nm laser) pump power. The results were obtained for a −25 dBm inputsignal at a wavelength of 1550 nm. It is seen that a gain of 19.5 dB,with the noise figure of 4 dB, can be achieved using a pump power of 150mW. In the invention, this same pump laser, with total maximum outputpower of 150 mW, is used to pump two EDWA's (621 and 622 of FIG. 6) withoptical characteristics similar to those shown in FIG. 7. Both EDWA'sare monolithically integrated on the same silicon substrate. The pumppower is split into two unequal portions, so that about 50 mW of poweris used to pump the EDWA serving as a pre-amplifier for the receiver,and about 100 mW of power is used to pump the EDWA serving as a boosteramplifier for the signal laser. Under these conditions, according toFIG. 7, one expects a pre-amplifier gain of about 16 dB and a noisefigure of 4.3 dB, resulting in a possible receiver sensitivityimprovement of about 11.5 dB. Simultaneously, again from FIG. 7, thebooster amplifier is providing small-signal gain of about 19 dB,although the actual gain experienced by the signal may be smaller due togain compression. Gain compression results from the existence of anoutput saturation power and is a function of input signal power, pumppower, and EDWA efficiency. For the EDWA used in generating theperformance charateristics of FIG. 7 the output saturation power wasabout 10 dBm. It follows that such an EDWA can be used in combinationwith a cheap signal laser (with maximum output power of less than 0 dBm)to boost its output power to a value of the order 10 dBm.

[0050] This integrated double-amplifier based on the EDWA technologytherefore enables one to achieve a much more compact and costefficient-solution for building a transceiver than any other currentlyconceived. First, one can use a cheaper low-power version of the signallaser instead of an expensive high-power counterpart. Second, one canuse a low cost PIN receiver instead of an expensive avalanche photodiode(APD). Third, the pump laser is shared between the two amplifiers, sothat its cost is not prohibitive. Fourth, the integrated EDWA chip iscompact and occupies less space than an EDFA. Fifth, hybrid integrationof lasers and PIN's with the EDWA chip further reduces the footprint ofthe module as shown in FIG. 6 leading to a smaller package and lowerpackaging costs.

[0051]FIG. 8 illustrates other examples of the invention. Red arrowsindicate inputs from the pump lasers, whereas green arrows indicateinputs and outputs for signal light. Example A shows a scheme where twopump lasers are used to pump an array of two amplifiers. The light fromthese lasers is first mixed and then split into two parts, one for eachamplifier. The 2^(nd) pump laser in this case is provided either forredundancy or to increase the pump power. Example B shows how the pumplaser can be coupled in the counter-propagating direction with respectto signal. Example C shows a redundantly-pumped amplifier array followedby a matching array of filters and variable optical attenuators. ExampleD shows how a single pump laser can be used to pump two amplifierswithout a splitter. In this example an unused portion of pump energy atthe end of the 1^(st) amplifier is coupled back onto the 2^(nd)amplifier. Example E shows how this approach can be used together withthe pump splitter in order to provide the most efficient usage of pumpenergy. Example F is similar to D, except that the same coupler is usedto couple out the signal light from the 1^(st) amplifier and couple inthe signal light to the 2^(nd) amplifier. The input and output positionsin these examples are not limited to the ones shown. In general, thereceiver and transmitter can be either on the same or on opposite sidesof the chip.

[0052] Other functional components can be included in a manner similarto the one shown in example C, and it is important to note that all ofthese can be manufactured using the same technology as that used for theproduction of an EDWA. Examples may include monolithic integration ofsuch elements as optical taps redirecting a small portion of signaloptical power towards a photodetector. The detector could be mountedeither on the edge of the chip or on its top; in the latter case aturning mirror is provided below the detector as described in U.S. Pat.Nos. 5,135,605 and 5,966,478. The purpose of the tap is to monitor theoutput power of the device and its gain. Still other elements mightinclude filters based on waveguide Mach-Zender interferometers, filtersbased on waveguide gratings, variable optical attenuators, modeconverters and others. Mode converters for example are often required tocombine two different waveguide media on the same substrate, asdescribed for example in U.S. Pat. No. 5,039,190.

[0053] The application of the amplifier array modules, however, may notbe limited to the realm of optical tranceivers. Other multichanneldevices may benefit from this invention, in particular those devices andsystems that require different operating conditions on each or some ofthe channels. For instance, a device with multiple channels, eachchannel being at a different signal wavelength such as in an arrayedwaveguide grating, will require an amplifier array in which eachamplifier is optimized for a specific wavelength. The optimization mayinvolve optimizing the lengths of individual amplifiers in the array,waveguide cross-sections, or individual pump powers. The variation ofoptical gain, or gain trimming, on each separate amplifier can also befacilitated by providing a variable optical attentuator at the end ofeach amplifier.

1. An integrated optical device for distributing optical pump energy,comprising: at least one input port for receiving optical energy; aplurality of output ports; and a user configurable optical networkcoupled to said input port for distributing said optical energy amongsaid output ports in a prescribed manner in conformance with auser-selected configuration.
 2. The optical device of claim 1 whereinsaid at least one input port comprises a plurality of input ports, saidoptical network further comprising at least one optical mixer opticallycoupled to said plurality of input ports, said optical mixer beingoptically coupled to the plurality of output ports for incoherentlymixing said optical pump energy among said plurality of output ports. 3.The optical device of claim 1 wherein said optical network furthercomprises at least one optical splitter optically coupled to the inputport, said optical splitter being optically coupled to the plurality ofoutput ports for distributing said optical energy among said outputports.
 4. The optical device of claim 1 wherein said optical networkfurther comprises at least one variable optical attenuator opticallycoupled to at least one of said ports for providing variable attenuationthereto.
 5. The optical device of claim 3 wherein said optical splitteris a variable optical splitter for dividing the optical pump energyamong the plurality of output ports in a user-prescribable manner. 6.The optical device of claim 1 wherein said optical network is formedfrom a planar lightwave circuit.
 7. The optical device of claim 2wherein said optical network is formed from a planar lightwave circuit.8. The optical device of claim 3 wherein said optical network is formedfrom a planar lightwave circuit.
 9. The optical device of claim 4wherein said optical network is formed from a planar lightwave circuit.10. The optical device of claim 1 further comprising at least tworare-earth doped optical waveguides for receiving the optical pumpenergy from the optical network.
 11. The optical device of claim 10wherein said at least two rare-earth doped optical waveguides defineindividual stages of a multistage optical amplifier in which opticalsignal power from one stage is coupled into the other stage.
 12. Theoptical device of claim 10 further comprising at least one pump sourcecoupled to the input port such that optical power is distributed fromsaid at least one pump source to said at least two rare-earth dopedoptical waveguides.
 13. The optical device of claim 10 wherein at leastone of the said optical rare-earth doped optical waveguides is a planarwaveguide.
 14. The optical device of claim 10 wherein at least one ofsaid optical rare-earth doped optical waveguides is a planar waveguideand the other optical rare-earth doped optical waveguide is a fiberwaveguide.
 15. The optical device of claim 10 wherein said rare-earthdoped optical waveguides are rare-earth doped optical fibers.
 16. Theoptical device of claim 10 further comprising at least one pump sourcecoupled to the input port such that optical power is distributed fromsaid at least one pump source to said at least two rare-earth dopedoptical waveguides, wherein said optical network is formed from a planarlightwave circuit.
 17. The optical device of claim 16 said opticalnetwork and said at least two rare-earth doped optical waveguides areformed on a common substrate.
 18. A planar optical device for providingoptical amplification, comprising: a first plurality of signal inputwaveguides each receiving an optical signal; at least one pump inputwaveguide receiving optical pump energy; a plurality of rare earth dopedwaveguides; a plurality of coupling waveguides respectively coupling theoptical signal and the optical pump energy to the plurality of rareearth doped waveguides; a plurality of output waveguides coupled to therare earth doped waveguides for providing a plurality of amplifiedoptical signals to an external element; and wherein said first pluralityof signal input waveguides, said at least one pump input waveguide, saidplurality of rare earth doped waveguides, said plurality of couplingwaveguides, and said plurality of output waveguides are planarwaveguides formed on at least one substrate.
 19. The planar opticaldevice of claim 18 wherein said first plurality of signal inputwaveguides, said at least one pump input waveguide, said plurality ofrare earth doped waveguides, said plurality of coupling waveguides, andsaid plurality of output waveguides are planar waveguides formed on acommon substrate.
 20. The planar optical device of claim 18 wherein saidfirst plurality of signal input waveguides, said at least one pump inputwaveguide, said plurality of rare earth doped waveguides, said pluralityof coupling waveguides, and said plurality of output waveguides areplanar waveguides respectively formed on a plurality of differentsubstrates.
 21. The planar optical device of claim 18 wherein at leasttwo of said plurality of rare earth doped waveguides are configured fordifferent performance applications.
 22. The planar optical device ofclaim 21 wherein said different performance applications include opticalpre-amplification and optical power amplification.
 23. The planaroptical device of claim 18 further comprising a waveguide splittercoupling the at least one pump input waveguide to the plurality ofrare-earth doped waveguides for splitting the optical pump energy with afixed splitting ratio.
 24. The planar optical device of claim 18 furthercomprising a plurality of variable optical attenuators respectivelylocated in said plurality of output waveguides for varying the opticalgain experienced by the amplified optical signals.
 25. The planaroptical device of claim 18 further comprising at least one pump sourcecoupled to the at least one pump input waveguide.
 26. The planar opticaldevice of claim 18 wherein said at least one pump input waveguidecomprises a plurality of pump input waveguides, and further comprising acommon pump source coupled to the plurality of pump input waveguides.27. The planar optical device of claim 25 wherein said pump source is amultimode laser.
 28. The planar optical device of claim 25 wherein saidpump source is a single mode laser.
 29. The planar optical device ofclaim 18 further comprising at least one signal laser transmittercoupled to at least one of the first plurality of signal inputwaveguides.
 30. The planar optical device of claim 18 further comprisingat least one receiver coupled to at least one of the plurality of outputwaveguides.
 31. The planar optical device of claim 25 further comprisingat least one receiver coupled to at least one of the plurality of outputwaveguides.
 32. The planar optical device of claim 18 wherein furthercomprising at least one optical isolator coupled to at least one of thesignal input waveguides.
 33. The planar optical device of claim 18further comprising a plurality of planar-waveguide mode transformersrespectively coupling said plurality of rare-earth doped waveguides tosaid plurality of coupling waveguides.
 34. The planar optical device ofclaim 19 wherein said plurality of rare earth doped waveguides areconfigured for different performance applications.
 35. The planaroptical device of claim 34 wherein said different performanceapplications include optical pre-amplification and optical poweramplification.
 36. The planar optical device of claim 18 furthercomprising a plurality of optical waveguide taps respectively coupled tothe said plurality of signal input waveguides and to said plurality ofoutput waveguides, said taps directing a portion of optical energy to atleast one photodetector.
 37. The planar optical device of claim 36wherein said at least one photodetector is mounted on said at least onesubstrate.
 38. An optical device for providing optical amplification,comprising: a first plurality of signal input waveguides each receivingan optical signal; at least one pump input waveguide receiving opticalpump energy; a plurality of rare earth doped waveguides, wherein atleast two of said plurality of rare earth doped waveguides areconfigured for different performance applications; a plurality ofcoupling waveguides respectively coupling the optical signal and theoptical pump energy to the plurality of rare earth doped waveguides; anda plurality of output waveguides coupled to the rare earth dopedwaveguides for providing a plurality of amplified optical signals to anexternal element.
 39. The optical device of claim 38 wherein saiddifferent performance applications include optical pre-amplification andoptical power amplification.
 40. The optical device of claim 38 whereinsaid differently configured rare earth doped waveguides have at leastone difference selected from the group consisting of cross-sectionaldimension, length, dopant concentration, and composition.
 41. Theoptical device of claim 38 wherein said first plurality of signal inputwaveguides, said at least one pump input waveguide, said plurality ofrare earth doped waveguides, said plurality of coupling waveguides, andsaid plurality of output waveguides are optical fiber waveguides. 42.The optical device of claim 38 wherein at least one waveguide, selectedfrom among said first plurality of signal input waveguides, said atleast one pump input waveguide, said plurality of rare earth dopedwaveguides, said plurality of coupling waveguides, and said plurality ofoutput waveguides, is an optical fiber waveguide.
 43. The optical deviceof claim 38 wherein said at least one pump input waveguide, saidplurality of rare earth doped waveguides, and said plurality of couplingwaveguides are planar waveguides formed on a common substrate.
 44. Theoptical device of claim 38 wherein said first plurality of signal inputwaveguides, said at least one pump input waveguide, said plurality ofrare earth doped waveguides, said plurality of coupling waveguides, andsaid plurality of output waveguides are planar waveguides respectivelyformed on a plurality of different substrates.
 45. The optical device ofclaim 38 further comprising a waveguide splitter coupling the at leastone pump input waveguide to the plurality of rare-earth doped waveguidesfor splitting the optical pump energy with a fixed splitting ratio. 46.The optical device of claim 38 further comprising a plurality ofvariable optical attenuators respectively located in said plurality ofoutput waveguides for varying the optical gain experienced by theamplified optical signals.
 47. The optical device of claim 38 furthercomprising at least one pump source coupled to the at least one pumpinput waveguide.
 48. The optical device of claim 38 wherein said atleast one pump input waveguide comprises a plurality of pump inputwaveguides, and further comprising a common pump source coupled to theplurality of pump input waveguides.
 49. The optical device of claim 47wherein said pump source is a multimode laser.
 50. The optical device ofclaim 47 wherein said pump source is a single mode laser.
 51. Theoptical device of claim 38 further comprising at least one signal lasertransmitter coupled to at least one of the first plurality of signalinput waveguides.
 52. The optical device of claim 38 further comprisingat least one receiver coupled to at least one of the plurality of outputwaveguides.
 53. The optical device of claim 38 further comprising atleast one optical isolator coupled to at least one of the signal inputwaveguides.
 54. The optical device of claim 38 further comprising aplurality of planar-waveguide mode transformers respectively couplingsaid plurality of rare-earth doped waveguides to said plurality ofcoupling waveguides.
 55. The optical device of claim 38 furthercomprising a plurality of optical waveguide taps respectively coupled tosaid plurality of signal input waveguides and to said plurality ofoutput waveguides, said taps directing a portion of optical energy to atleast one photodetector.
 56. The optical device of claim 55 wherein saidfirst plurality of signal input waveguides, said at least one pump inputwaveguide, said plurality of rare earth doped waveguides, said pluralityof coupling waveguides, said plurality of output waveguides, and said atleast one photodetector are mounted on at least one substrate.
 57. Amethod of distributing optical pump energy, comprising: receivingoptical pump energy at an input of an optical network; and configuringthe optical network for distributing the optical pump energy among aplurality of output ports in a prescribed manner.
 58. The method ofclaim 57 further comprising the step of incoherently mixing said opticalpump energy among said plurality of output ports.
 59. The method ofclaim 57 further comprising the step of coherently distributing saidoptical energy among said output ports.
 60. The method of claim 57further comprising the step of providing variable attenuation to asignal traversing at least one of said ports.
 61. The method of claim 57wherein the optical energy is distributed among said output ports in auser-prescribable manner.
 62. The method of claim 57 wherein saidoptical network is formed from a planar lightwave circuit.
 63. Themethod of claim 57 further comprising the step of providing the opticalpump energy from the optical network to at least two rare-earth dopedoptical waveguides.
 64. The method of claim 63 wherein said at least tworare-earth doped optical waveguides define individual stages of amultistage optical amplifier in which optical signal power from onestage is coupled into the other stage.
 65. The method of claim 63further comprising at least one pump source coupled to the input of theoptical network such that optical power is distributed from said atleast one pump source to said at least two rare-earth doped opticalwaveguides.
 66. The method of claim 63 wherein at least one of the saidoptical rare-earth doped optical waveguides is a planar waveguide. 67.The method of claim 63 wherein at least one of said optical rare-earthdoped optical waveguides is a planar waveguide and the other opticalrare-earth doped optical waveguide is a fiber waveguide.
 68. The methodof claim 65 said optical network and said at least two rare-earth dopedoptical waveguides are formed on a common substrate.
 69. A method ofamplifying optical signals, comprising: directing a first optical signaland optical pump energy to a first rare-earth doped waveguide forproviding optical gain to the first optical signal, said firsterbium-doped waveguide being formed on a planar substrate; directing asecond optical signal and optical pump energy to a second rareearth-doped waveguide for providing optical gain to the second opticalsignal, said second waveguide being formed on said planar waveguide; andsplitting the optical pump energy received from a pump source prior todirecting it to the first and and second erbium-doped waveguides. 70.The method of claim 69 wherein said first and second rare earth dopedwaveguides are configured for different performance applications; 71.The optical device of claim 70 wherein said different performanceapplications include optical pre-amplification and optical poweramplification.
 72. The optical device of claim 70 wherein saiddifferently configured rare earth doped waveguides have at least onedifference selected from the group consisting of cross-sectionaldimension, length, dopant concentration, and composition.
 73. The methodof claim 69 wherein the step of splitting is performed with a splitterformed on said planar waveguide.
 74. The method of claim 69 furthercomprising the step of attenuating of the first and second opticalsignals after being amplified.
 75. The method of claim 69 furthercomprising the step of supplying the optical pump energy from at leastone pump source located on said planar substrate.
 76. The method ofclaim 75 wherein said pump source is a multimode laser.
 77. The methodof claim 75 wherein said pump source is a single mode laser.
 78. Themethod of claim 69 further comprising the step of transmitting the firstand second optical signals to the first and second rare-earth dopedwaveguides from at least one signal laser transmitter.
 79. The method ofclaim 69 further comprising the step of directing one of said first andsecond optical signals from one of said rare-earth doped waveguides toat least one receiver.
 80. The method of claim 78 further comprising thestep of directing one of said first and second optical signals from oneof said rare-earth doped waveguides to at least one receiver.
 81. Themethod of claim 69 further comprising the step of transforming a mode ofat least one of said first and second optical signals received from oneof said rare-earth doped waveguides
 82. The method of claim 37 whereinthe directing steps include the steps of directing a portion of at leastone of the first and second optical signals to at least onephotodetector.
 83. The method of claim 82 wherein said at least onephotodetector is mounted on said planar substrate.
 84. The opticaldevice of claim 1 further comprising at least two optical waveguidesdoped with optically active elements for receiving the optical pumpenergy from the optical network
 85. The method of claim 57 furthercomprising the step of providing the optical pump energy from theoptical network to at least two optical waveguides doped with opticallyactive elements.